John Lewis shouted, "I'm sorry, Mrs. Cassidy" after the widow of Officer Chuck Cassidy recounted their final conversation during testimony Wednesday.
Judy Cassidy told jurors she spoke to her husband less than an hour before Lewis fatally shot him on Oct. 31, 2007.
The 23-year-old defendant pleaded guilty last week to a general charge of murder. A jury is hearing testimony to decide if he will be convicted of first- or second-degree murder.
Lewis admitted he shot Cassidy in the head when the officer walked in on a doughnut shop robbery. Cassidy died a day later.
Closing arguments are scheduled for Thursday.